Energy and Power in Electric Circuits – Learn
Potential difference is defined as the work done to move a charge against an electric field between two points. The equation relating potential difference and work is:
or 
Where:
= voltage (in V)
= work (in J)
= charge (in C)
The rate at which energy is used or converted into other forms of energy over a period of time is known as its electrical power. Power (P) is the rate at which energy is transformed in a circuit component, and is measured in watts (W). Power is calculated using:
Where:
= power (in W)
These equations are often rearranged to give the relationship:
Example 1:
Calculate the work carried by 4C of charge with a potential difference of 12V:
Answer:
Using:
Example 2:
A speaker operating on a voltage of 18V draws a current of 3A. Calculate the power used by this speaker:
Answer:
Using 
Example 3:
A potential difference of 6V is used to produce a current of 150mA in a set of headphones for 10 minutes. How much energy is used in this time?
Answer:
Using: 
